Not Applicable
Not Applicable
1. Field of the Invention
The present invention relates generally to a method of installing a stent utilizing a balloon catheter to perform an initial angioplasty and to seat the stent after it has been located in the vessel. The invention also relates to novel balloon structures which have particular use in the method of the invention. More specifically, this invention relates to a stent delivery system wherein at least a portion of the balloon is step compliant which provides the balloon with the ability to expand specific portions of the balloon at different times according to a variety of inflation pressures. In addition the unique shape of the balloon may be configured to engage the stent throughout the insertion as well as the delivery procedures which in turn reduces longitudinal movement of an associated medical device such as a stent, stent-graft, graft or vena cava filter mounted on the balloon both prior to and during balloon expansion.
2. Description of the Related Art
Expandable, implantable medical devices such as stents are utilized in a number of medical procedures and situations as are stent delivery assemblies. As such, their structure and function are well known. A stent is a generally cylindrical prosthesis introduced via a catheter into a lumen of a body vessel in a configuration having a generally reduced diameter and then expanded to the diameter of the vessel. The stent may be self-expanding, such as a NITINOL shape memory stent, or it may be expandable by means of an inflatable portion of the catheter, such as a balloon. In its expanded configuration, the stent supports and reinforces the vessel walls while maintaining the vessel in an open, unobstructed condition.
Self-expanding, inflation assisted expandable and inflation expandable stents are well known and widely available in a variety of designs and configurations. Inflation expandable and inflation assisted expandable stents are expanded via outward radial pressure such as that provided by a balloon disposed underneath the stent during inflation of the balloon.
Medical device delivery balloons may have a variety of shapes, sizes, inflation characteristics and a variety of other performance attributes. Some examples of balloons which may be used for the expansion and delivery of a medical device are described in U.S. Pat. Nos. 5,556,383; 5,738,901; 6,024,752; and 6,048,350.
In advancing an inflation expandable stent through a body vessel to the deployment site, there are a number of important considerations. The stent must be able to securely maintain its axial position on the delivery catheter, without translocating proximally or distally, and especially without becoming separated from the catheter. Furthermore, it may be desirable to protect the distal and proximal ends of the stent to prevent distortion of the stent and to prevent abrasion and/or to reduce potential trauma to the vessel walls.
To address the concerns stated above, one approach has been identified which utilizes a retractable sheath or sheaths which are disposed about the distal end of the catheter and cover the stent and balloon. In such devices the sheath is retracted prior to the inflation of the balloon and subsequent delivery of the stent. Another solution involves the utilization of one or more stent retaining means such as elastomeric sleeves or socks. The socks are disposed about the ends of the stent and the respective adjacent portions of the catheter shaft. Socks may be constructed such that during balloon inflation the socks release the stent as a result of the forces and change in geometry resulting from the expanding balloon. It is also known that socks may be constructed to retract or be pulled off of the stent as a result of their construction and the expansion of the balloon.
Inflation expandable stent delivery and deployment assemblies are known which utilize restraining means that overlie the stent during delivery. U.S. Pat. No. 4,950,227 to Savin et al., relates to an inflation expandable stout delivery system in which a sleeve overlaps the distal or proximal margin (or both) of the stent during delivery. During inflation of the stent at the deployment site, the stent margins are freed of the protective sleeve(s). U.S. Pat. No. 5,403,341 to Solar, relates to a stent delivery and deployment assembly which uses retaining sheaths positioned about opposite ends of the compressed stent. The retaining sheaths of Solar are adapted to tear under pressure as the stent is radially expanded, thus releasing the stent from engagement with the sheaths. U.S. Pat. No. 5,108,416 to Ryan et al., describes a stent introducer system which uses one or two flexible end caps and an annular socket surrounding the balloon to position the stent during introduction to the deployment site. The content of all references, including patents and patent applications are respectively incorporated it their entirety heroin by reference.
Providing a means for containing and securing the stent or other medical device on the balloon catheter prior to inflation is but one problem facing stent delivery systems. An additional concern is the shifting or sliding of the stent relative to the balloon during balloon expansion. Numerous attempts have been made to reduce or prevent translocation of the stent on the balloon during balloon expansion. For example: copending U.S. patent application Ser. No. 09/667,916, filed Sep. 22, 2000 and entitled Coated Stents with Better Gripping Ability, describes a stent coating which provides the stent with improved ability to adhere to the balloon during the expansion process. Another example is U.S. Pat. No. 5,836,965 which describes a process wherein a balloon is expanded and heat set then allowed to cool in order to adhere the balloon to the stent. Yet another example is co-pending U.S. patent application Ser. No. 08/740,727, filed Nov. 1, 1996 and entitled Selective Coating Of A Balloon Catheter With Lubricous Material For Stent Deployment, which describes a balloon having a tacky coating for securing a stent to a balloon prior to delivery.
Angioplasty, an accepted and well known medical practice involves inserting a balloon catheter into the blood vessel of a patient, maneuvering and steering the catheter through the patient""s vessels to the site of the lesion with the balloon in an uninflated form. The uninflated balloon portion of the catheter is located within the blood vessel such that it crosses the lesion or reduced area. Pressurized inflation fluid is metered to the inflatable balloon through a lumen formed in the catheter to thus dilate the restricted area. The inflation fluid is generally a liquid and is applied at relatively high pressures, usually in the area of six to twenty atmospheres. As the balloon is inflated it expands and forces open the previously closed area of the blood vessel. Balloons used in angioplasty procedures such as this are generally fabricated by molding and have predetermined design dimensions such as length, wall thickness and nominal diameter. Balloon catheters are also used in other systems of the body for example the prostate and the urethra. Balloon catheters come in a large range of sizes and must be suitably dimensioned for their intended use.
Recently the use of a catheter delivered stent to prevent an opened lesion from reclosing or to reinforce a weakened vessel segment, such as an aneurism, has become a common procedure. A typical procedure for stent installation involves performing an initial angioplasty to open the vessel to a predetermined diameter sufficient to permit passage of a stent delivery catheter across the lesion, removal of the angioplasty balloon catheter, insertion of a delivery catheter carrying the stent and a stent deploying mechanism, deploying the stent across the opened lesion so as to separate the stent from the catheter and bring it into contact with the vessel wall, usually with dilation to a lager diameter using a balloon larger than the balloon of the predilation catheter, and then removing the delivery catheter (after deflating the balloon if used). In many cases it has become the practice to then xe2x80x9cretouchxe2x80x9d the dilation by deploying a third catheter carrying a balloon capable of dilating at a substantially higher pressure to drive the stent into the vessel wall, thereby to assure that there is no risk of the stent later shifting its position and to reduce occurrence of restenosis or thrombus formation. This third xe2x80x9cretouchxe2x80x9d dilation is often considered necessary when the balloon used to seat the stent is made of a compliant material because such balloons generally cannot be safely pressurized above 9-12 atm., and higher pressures are generally considered necessary to assure full uniform lesion dilation and seating of the stent.
A wide variety of stent configurations and deployment methods are known. For instance, stent configurations include various forms of bent wire devices, self-expanding stents; stents which unroll from a wrapped configuration on the catheter; and stents which are made of a deformable material so that the device may be deformed on deployment from a small diameter to a larger diameter configuration. References disclosing stent devices and deployment catheters include:
In U.S. Pat. No. 5,348,538, the entire contents of which being incorporated herein by reference, there is described a single layer balloon which follows a stepped compliance curve. The stepped compliance curves of these balloons has a lower pressure segment following a first generally linear profile, a transition region, typically in the 8-14 atm range, during which the balloon rapidly expands yielding in elastically, and a higher pressure region in which the balloon expands along a generally linear, low compliance curve. The stepped compliance curve allows a physician to dilate different sized lesions without using multiple balloon catheters.
Stepped compliance curve catheter balloon devices using two different coextensively mounted balloon portions of different initial inflated diameter, are also described in U.S. Pat. No. 5,447,497 and in U.S. Pat. No. 5,358,487 to Miller. These dual layer balloons are designed with the outer balloon portion larger than the inner portion so that the compliance curve follows the inner balloon portion until it reaches burst diameter and then, after the inner balloon bursts, the outer balloon becomes inflated and can be expanded to a larger diameter than the burst diameter of the inner balloon.
A polyethylene ionomer balloon with a stepped compliance curve is disclosed in EP 540 858. The reference suggests that the balloon can be used on stent delivery catheters. The disclosed balloon material of this reference, however, yields a compliant balloon and therefore a stent delivered with such a balloon would typically require xe2x80x9cretouch.xe2x80x9d
Balloons having a stepped compliance curve have also been described for use in stent delivery. Two examples of such stent delivery balloons and methods of their use are described in U.S. Pat. No. 5,749,851 and U.S. Pat. No. 5,980,532, respectively incorporated in their entirety herein by reference.
The entire content of all of the patents and patent applications listed within the present patent application are respectively incorporated in their entirety herein by reference.
The invention in one aspect is directed to a medical balloon. More specifically, the present invention is directed to a stent delivery system employing a unique stepped compliant balloon which is shaped to retain a stent about a stent mounting region of the balloon prior to and during stent delivery. The balloon is capable of providing low pressure predilation at a relatively small diameter to open the lesion sufficiently to allow insertion and deployment of the stent across the lesion and for subsequent high pressure embedding of the stent in the vessel wall. The same balloon catheter may also be employed to insert and deploy the stent. Thus at least one catheter may be eliminated from what may otherwise be a two or three catheter installation process.
In at least one embodiment of the invention, the balloon of the invention may be made by molding a balloon into a configuration in which the second portion has a larger diameter than the first portion and then shrinking the second portion to the diameter of the first portion or less than the diameter of the first portion. The method of making such balloons comprises yet another aspect of the invention.
In at least one embodiment of the invention, the balloon may be incorporated into a stent delivery catheter, wherein a stent mounting region of the balloon has a diameter less than the diameter of the balloon ends, whereby the stent is prevented from longitudinal migration relative to the catheter as a result of interference provided by the balloon ends. The balloon may be configured to expand so that the stent remains held in place during balloon expansion.
In at least one embodiment of the invention the balloon is configured to have a first inflation state, a second inflation state, and a third or fully inflated state.
In yet another embodiment of the invention the balloon may be configured to expand such that the balloon ends maintain a larger diameter than the stent mounting region until a predetermined inflation pressure is achieved, whereupon the stent mounting region may expand to a diameter greater than the diameter of the balloon ends.
In yet another aspect of the invention a stent delivery catheter may employ a stepped compliant balloon and one or more stent retaining sleeves. The balloon may be configured such that the balloon ends inflate sufficiently to cause the sleeves to retract, whereupon the stent mounting region expands to release the stent.
These and other more detailed and specific objectives and an understanding of the invention will become apparent from a consideration of the following Detailed Description of the Invention in view of the Drawings. Other embodiments may also be apparent, but which are not described in detail, from the following description.